The present invention concerns a method of detecting a fault in a monitored section of an electric transmission line using the distance protection principle, where a release signal and a direction signal are generated in the event of a fault by one measuring unit at each end of the line section monitored using current and voltage values measured on the monitored section of electric transmission line, and the direction signal is transmitted to the other measuring unit over a low-transmission-capacity data line running between the measuring units.
Siemens Handbook xe2x80x9c7SA511 V3 Digitaler Abszwergschutzxe2x80x9d (7SA511 V3 Digital Feeder Protection) describes a method for reliably detecting a fault on a monitored section of an electric transmission line, in the event of a fault, a release signal is generated at both ends of the monitored section of line using the distance protection principle, thereby prompting a circuit-breaker to isolate that section from the electric transmission line. Since a fault can be detected reliably from each end of the monitored section of line over only approximately 80% of the length of the monitored section of line by the distance protection method in the event of a fault, a direction signal is generated with the known method at each end of the monitored section of line in the event of a fault, with the information that the fault lies in the direction of the other end. The direction signal is transmitted over a data transmission line to the other end and to the other measuring unit. Since the direction signal is a simple binary signal or is transmitted serially, a simple line with a low transmission capacity is used as the data transmission line. With the direction signal received, a fault on the monitored section of line can be detected with a high reliability, taking into account the direction signal generated at the other end, even if the fault has occurred in the end area or the initial area of the monitored section of line.
European Patent Application No. 0 275 779 describes a protective arrangement in which a directional relay is present at each end of the monitored line section. The directional relays at the ends of the monitored section of line are linked together by a wireless transmission channel to permit signal exchange.
In addition, European Patent Application No. 0 358 488 describes a protective circuit within which fault-relevant current and voltage quantities are measured at each end of a monitored section of line and exchanged between the two ends over a data connection. At each end there is a microprocessor which determines the location of a fault with measured current and voltage quantities that are relevant to the fault.
Furthermore, Unexamined German Patent No. 2 112 136 describes an arrangement for monitoring a section of an electric transmission line equipped with a distance protection system on each end of the section of line to be monitored. The arrangement also has a circuit for measuring the distance to the fault location. At each end of the monitored section of line, the circuit has a memory in which current and voltage values derived from the electric transmission line are stored after analog-digital conversion. In the event of a fault on the monitored section of line, the values stored in the memory are transmitted over a data transmission system to an analysis unit with a downstream computer to locate the fault on the monitored section of line. The data transmission system must be of a relatively high quality here, because a relatively large volume of data must be transmitted.
An object of the present invention is to provide a method of detecting a fault on a monitored section of an electric transmission line with which not only is it possible to generate a release signal by the distance protection principle, but also a measured quantity indicating the location of the fault on the monitored section of line can be generated by a simple procedure.
To achieve this object in accordance with the present invention, intermediate parameters suitable for calculating the location of the fault are produced in each measuring unit after the release signal is generated and are transmitted over the data transmission line to the other measuring unit. A measured quantity indicating the location of the fault is derived in each measuring unit from its own intermediate parameter and the transmitted intermediate parameter.
An important advantage of the method according to the present invention is that no additional data transmission system is needed to accurately determine the location of the fault, but instead the data transmission line used for transmitting the direction signals in the distance protection measurement can be used. No additional (expensive) data transmission system is needed for locating faults. Therefore, the data transmission line can be used for locating faults because it is no longer needed after tripping and after the direction signals have been sent. This is made possible by the fact that according to the present invention, intermediate parameters suitable for calculating the location of faults are formed in the measuring units for locating faults. These intermediate parameters can be transmitted readily over the low-transmission-capacity data line.
In the method according to the present invention, different intermediate parameters can be produced. It is regarded as advantageous if a measured impedance quantity characteristic of a particular fault location is supplied as the intermediate parameter in each measuring unit. With appropriate design, the measuring unit is capable of accurately measuring the location of the fault only from the impedance quantity transmitted from the other measuring unit. This type of fault locating is described in Cook, V. et al., Fundamental Aspects of Fault Location Algorithms Used in Distance Protection, IEEE Proceedings, Vol. 133, Pt. C, No. 6, September 1986.
In another advantageous embodiment of the method according to the present invention, characteristic current and voltage vectors for the particular fault location are supplied as intermediate parameters in each measuring unit. Such intermediate parameters can also be transmitted over a low-transmission-capacity data line. Such a method of locating faults is also described in Johns, A. et al., Accurate Fault Location Technique for Power Transmission Lines,xe2x80x9d IEEE Proceedings, Vol. 137, Pt. C, No. 6, November 1990.